1. Field of the Invention
The present invention generally relates to a communication method, a communication system, and a communication apparatus and particularly to a communication method, a communication system, and a communication apparatus having a base station for calling and a terminal for returning a response to the calling from the base station.
2. Description of the Related Art
In an electronic shelf label system, an electronic shelf label having rewritable display information is registered in a host computer and then attached to a product shelf. It is possible to rewrite the display information of the electronic shelf label from the host computer by accessing the electronic shelf label through an access point (refer to Patent Documents 1 to 5).
Such an electronic shelf label system employs a communication system in which a communication channel for communication between the electronic shelf label and an access point is determined using a beacon. For example, in CSMA/CA employed in IEEE 802.11b and the like, each terminal performs carrier sensing so as to confirm that a radio channel is continuously available for a certain period of time (random) and then transmits data. In accordance with this, collision is avoided.
Patent Document 1: Japanese Laid-Open Patent Application No. 2002-304673
Patent Document 2: Japanese Laid-Open Patent Application No. 2005-99888
Patent Document 3: Japanese Laid-Open Patent Application No. 2002-109177
Patent Document 4: Japanese Laid-Open Patent Application No. 2004-265196
Patent Document 5: Japanese Laid-Open Patent Application No. 9-138892
In view of this, a conventional method has a problem in that when the number of terminals is very large or when an amount of data transmitted by the terminal is very small, each terminal stands by while performing carrier sensing for a longer period of time in comparison with a period of actual data transmission, so that this is inefficient in terms power saving, for example.